1. Field of the Invention
The present invention relates to a method of and apparatus for making a three dimensional object in which a target object is obtained by sintering and hardening powder material with an optical beam.
2. Description of the Related Art
Japanese Patent No. 2620353 discloses a method of making a three-dimensional object known as photo-shaping. According to this Patent, as shown in FIG. 21A, an optical beam L is first irradiated on a predetermined portion of a layer of powder material, which is either an organic material or an inorganic material, to form a sintered layer 11. The sintered layer 11 thus obtained is then covered with a new layer of powder material, and the optical beam L is irradiated on a predetermined portion of the new layer to form a new sintered layer 11, which is united with the underlying layer 11. These processes are repeatedly carried out to form a sintered article or three-dimensional object in which a plurality of sintered layers 11 are firmly laminated one above another. According to this method, the irradiation of the optical beam L is conducted based on sectional form data of each of the layers that are obtained by slicing a model of design data (CAD data) of the three-dimensional object into a desired thickness. For this reason, without a CAM device, the method referred to above can be used to make a three-dimensional object of an arbitrary shape and to obtain any shaped object of a desired shape quickly, compared with a method with the use of cutting work.
According to this method, however, as shown in FIG. 21A, unnecessary powder 15 adheres to the sintered and hardened portions due to heat transmitted therefrom, thereby forming a surface layer 16 of a low density on the shaped object.
Japanese Laid-Open Patent Publication (unexamined) No. 2000-73108 discloses removing stepped outer portions as shown in FIG. 21B that result from the lamination of the sintered layers 11. However, even if the stepped outer portions have been removed, as shown in FIG. 21C, the low-density surface layer 16 still remains and, hence, no smooth outer surface can be obtained.
Furthermore, unless the sintered layers are caused to have a sufficient density (for example, a porosity less than 5%) during the sintering, removal of the stepped outer portions does not result in a smooth outer surface because pores appear on the surface of the sintered layers even after such removal.
Also, where the shaped object is finished for removal of the low-density surface layer after the shaping, there are some limits to finishing tools depending on the shape of the shaped object. By way of example, it becomes occasionally impossible to cut relatively deep and narrow grooves because small-diameter tools have a limit in length. In this case, additional electric discharge machining is required, giving rise to problems in terms of time and cost.
In addition, because the entire three-dimensional object is made by the powder-sintering method, or because each powder layer is sintered by irradiating a laser beam thereto, it sometimes takes a long time depending on the shape of the three-dimensional object to be made.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide an improved method and apparatus capable of making a three-dimensional object in a short time.
Another objective of the present invention is to provide the method and apparatus of the above-described type, which is capable of finishing the object surface smoothly at a low cost irrespective of the shape thereof.
In accomplishing the above and other objectives, the method according to the present invention includes the steps of: (a) irradiating an optical beam on a predetermined portion of a powder layer to form a sintered layer; (b) covering the sintered layer with a new powder layer; (c) irradiating the optical beam on a predetermined portion of the new powder layer to form another sintered layer that has been united with the underlying sintered layer; (d) repeating the steps (b) and (c) to form a plurality of sintered layers united together, which have a size greater than that of a target shape of the three-dimensional object; and (e) removing a surface region of a shaped object formed by then during the step (d).
Because the step (e) is carried out during the step (d), it becomes possible to finish the object surface without any restrictions by the size of a finishing machine such as the length of a drill or the like.
The method according to the present invention may further include, prior to the step (a), the steps of: (a1) placing on a sintering table a base that constitutes a lower structure of the three-dimensional object; (a2) machining the base; and (a3) aligning the base with a laser beam irradiating position.
The provision of the base dispenses with the formation and the sintering of a certain number of powder layers corresponding to the thickness of the base, making it possible to reduce the time required for making a three-dimensional object that has been hitherto made via a number of sintering processes. The provision of the base is also effective to make a three-dimensional object having narrow grooves of a high aspect ratio.
Prior to the step (a1), the time required for machining the base is compared with the time required for forming a plurality of sintered layers of a same shape as the base, and if the former is determined to be shorter than the latter, the base is made.
If the base has a recess in which some of the sintered layers are formed or an even surface on which a lowermost sintered layer is formed, the bonding strength between the base and the sintered layers can be increased.
It is preferred that the surface region removed has a thickness greater than a thickness of a low-density surface layer created by adhesion of powder material to the sintered layers. By so doing, the object surface can be smoothly finished.
If the sintered layers are exposed by the removal of the surface region, the exposed surface has a high density and is hence smooth.
Where the removal of the surface region is carried out by cutting, it is preferred that an optical beam be irradiated on a portion to be removed to soften it, prior to the step (e). The irradiation of the optical beam acts to reduce the cutting force, making it possible to reduce the cutting time and prolong the life of a cutting tool.
The removal of the surface region may be carried out by a laser.
Advantageously, after the step (e), an optical beam is irradiated on a portion of the shaped object from which the surface region has been removed, thereby increasing the density of such portion.
Again advantageously, unsintered powder around the sintered layers or swarf produced by the removal of the surface region is removed during the step (e). By so doing, a new powder layer formed after that is not adversely affected by such swarf.
The unsintered powder around the sintered layers may be removed prior to the step (e). In this case, because no swarf does not mix with the unsintered powder, the unsintered powder can be reused.
After the step (e), a space from which the unsintered powder or swarf has been removed may be filled with resin or wax. The use of resin or wax makes it possible to reduce the amount of powder when a new powder layer is subsequently formed.
Prior to the step (e), the unsintered powder may be solidified by freezing or using resin or wax. In this case, no refilling of powder material is required, and only the swarf can be removed without difficulty.
On the other hand, the apparatus according to the present invention includes a powder layer-forming unit for forming a powder layer, a sintered layer-forming unit for forming a sintered layer by irradiating an optical beam on a predetermined portion of the powder layer, a distance regulator for regulating a distance between the sintered layer-forming unit and the sintered layer, and a surface layer-removing unit for removing a surface layer of a density lower than that of the sintered layer.
The apparatus of the above-described construction contributes to improve the quality of the object surface.
The apparatus may further include a discharge unit held in close proximity to the powder layer-forming unit for discharging unsintered powder or swarf produced by the surface layer-removing unit. The discharge unit acts to prevent a new powder layer from being adversely affected by the swarf.
The discharge unit may have a drive unit that acts to move the discharge unit along a contour line of each plane to be shaped.